As today’s story on the historically long odds James Holmes faces in his insanity plea for the Aurora theater shootings notes, Colorado is one of only 11 states in the country that places the burden of proving sanity on the prosecution.

Thirty-five states say it is up to the defendant to prove insanity. Four states — Kansas, Utah, Idaho and Montana — have abolished the insanity defense altogether or have a “guilty but insane” verdict.

Every person is presumed to be sane; but, once any evidence of insanity is introduced, the people have the burden of proving sanity beyond a reasonable doubt.

Why did Colorado decide to do things that way? Just because.

The prosecution’s burden of proving insanity has been in state law for generations. As a Colorado Supreme Court decision from 1940 notes, the not guilty by reason of insanity plea has been explicitly in state law since 1927. Before that, defendants could raise insanity claims under a basic not guilty plea. The burden was always on the prosecution to prove sanity.

“Now, as formerly,” the state Supreme Court wrote in a 1933 ruling, “when the question is properly raised, the burden is upon the people to prove beyond a reasonable doubt that the defendant, when he committed the act charged, was sane.”

That’s not the way other states did it. In 1968, when the state Supreme Court took up the burden-of-proof issue in a seminal ruling, the dissenting opinion by Justice Robert H. McWilliams listed 24 states that put the burden on the defendant. As McWilliams noted, Oregon’s law had required the defendant to prove insanity since 1864.

The justices in that ruling — Juhan v. District Court — were grappling with the constitutionality of a law the legislature passed to shift the burden from the prosecution to the defense. McWilliams argued that the federal courts were OK with the burden being on the defendant, and he said that the placement of the burden on the prosecution held no special significance:

It is perhaps of historical interest to note that when this court by judicial decision adopted the rule that the People had the burden of proof in this regard it was not on any basis that “due process” required such a rule. On the contrary, it was simply on the basis that such rule was then believed to be “the better doctrine” and as of that time, at least, represented the so-called “weight of authority.” … I contend that this court, or the General Assembly, could have gone “either way” on the question[.]

But McWilliams was greatly outnumbered; only one other justice joined his dissent. The majority, led by Chief Justice Ostis Otto Moore, ruled that it is fundamental to courtroom fairness that the prosecution has the burden of proof in criminal cases — whether the proof is for guilt or sanity. And it didn’t matter what other states had done or what the federal courts had ruled OK. This was about what was right for Colorado. Moore wrote:

It cannot be done … for the very simple reason that in this state our concept of due process of law prohibits it.

McWilliams was steamed, writing in his dissent that the decision was the first time any court in the country had ruled in a published decision that requiring a defendant to prove insanity was unconstitutional. But the 1968 decision stood, and it remains precedent today.

And it continues to have real consequences.

In this year’s legislative session, state Rep. Frank McNulty, R-Highlands Ranch, introduced a bill to again try to put the burden of proof on a defendant claiming insanity. McNulty said he came up with the idea while listening to a radio report on Holmes’ case.